The present invention relates to a device for measuring movement within a structure, and more particularly to a device for measuring relative movement between two portions of a structure.
It is often desirable to monitor the movement of the components of a structural assembly. A history of the movement provides information indicative of structural integrity, strains, stresses, loads, fatigue, and rigidity. Particularly important is the observation of two portions of a structure relative one another, such as the movement of a masonry wall along a break or fault in the wall. As referred to in this application, masonry concrete, stone, brick, or any other type of structural wall typically poured or laid. By monitoring movement of the masonry wall along the crack, one can determine the problems causing the wall movement and take appropriate corrective action to properly prevent further deterioration.
Although several devices are known for measuring the movement of a masonry wall along a fault, these devices are not without their drawbacks. One such device is manufactured by Avongard Products of England under the trademark TELL-TALE. The TELL-TALE device includes a first arm securable to the wall on one side of the fault and a second arm securable to the wall on the other side of the fault. Each arm includes a transparent portion defining a Cartesian grid with the grids superimposed over one another. Movement of the wall on either side of the fault causes the grids to shift relative one another providing a crude indication of relative wall movement. However, the TELL-TALE device does not provide the desired accuracy of measurement. The superimposed Cartesian grids are difficult both to read and to subsequently analyze the derive information regarding both the angular and linear movement of the one wall portion with respect to the other.
A second method of detecting wall movement is to secure two straight rulers on either side of the crack perpendicular one another across the crack. As the wall portions move, the rulers will provide a crude indication of relative wall movement. However, calculation of wall movement based on ruler positions is, to say the least, difficult, if not impossible. Further, the straight rulers can be easily bumped or nudged off the wall requiring the entire process to be restarted.
Other mechanical devices for detecting structural movement involve specially calibrated, demountable dial micrometers which measure between pins, or discs, affixed to the wall and across the crack in a triangular pattern. These devices, however, are very expensive; and furthermore, are subject to operator error and "background noise" problems because they are too sensitive.